This invention relates generally to drag type drill bits and more particularly to improved cooling and cleaning means for cutting elements on a drag type drill bit.
The two main problems encountered in drilling which tend to deteriorate bits or to result in decreased penetration of a formation, are deterioration of the bit face resulting from heat degradation, and "balling". Balling is caused by a sticky formation, such as sticky shales or similar formations having a large percentage of clays, adhering to the cutting face of the bit. This may occur in certain formations, for example, where the hydraulic action of the drilling mud is inadequate or where hydraulic passages in the bit may be poorly designed which result in an inefficient cross-flow of mud across the face of the bit. It is noted that for drilling offshore the continental United States, water base muds are normally employed as government regulations generally render the use of oil base muds cost prohibitive. The use of water base muds results in a substantial balling, particularly when drilling in sticky shales or similar formations. One reason for this effect is believed to be the swelling effect of the water on the clays of the shale material as the drag-type drill bits have cutting elements which are prone to clogging or balling up.
It has become common to provide drag-type rotary drill bits with cutting elements projecting from the outer bit surface made of polycrystalline (man-made) diamond compacts or cutters ("PDC") on inserts or studs secured within openings in the bit body. A drag-type bit actually cuts or chips the earth formation instead of crushing the formation as in a normal cone-type roller drill bit. The use of diamond in cutting elements is especially important in drag-type bits in order to increase their life. The polycrystalline diamond material typically is provided in the form of a relatively thin layer of around 0.020 inch, for example, on one face of a disc formed of tungsten carbide. The disc is normally secured, such as by brazing, to the body of a stud to form an insert which fits within a bore or recess in the body of the drag type drill bit.
The disc with the diamond face and tungsten carbide base which may be around one-eighth (1/8) inch in thickness, for example, as well known in the art, is manufactured by the Specialty Material Department of General Electric Company at Worthington, Ohio and sold under the trademark "Stratapax". A series of inserts are normally secured within openings in the face of the drag bit body in an interference fit or by brazing. However, inserts other than diamond studded inserts may be provided, such as, for example, tungsten carbide inserts.
It is highly desirable that means be provided to cool and clean each of the bit inserts while they are working in the bore hole. As shown in U.S. Pat. No. 4,303,136 dated Dec. 1, 1981, each diamond or stud insert in a diamond drag bit has an individual flow passage therefor in front of the diamond cutting face of the insert, thereby to assure cooling and cleaning of each insert in the face of the drag bit. The drilling fluid discharged from the fluid passageway directs the hydraulic mud around the synthetic diamond cutting face of the stud body.
Further, as shown in U.S. Pat. No. 4,452,324 dated June 5, 1984, discharge nozzles are shown for cutting faces in a rotary drill bit. However, it has been common and accepted practice to direct the jet or stream of drilling fluid from the nozzles toward the cutting faces as it has been felt that by directing the fluid toward the cutting face an improved cleaning action is effected. One result of such a jet or stream of drilling fluid toward the cutting face is that the cuttings are directed by the jet toward the outermost portion of the cutting edge adjacent the formation, which is believed to reduce the cutting efficiency of the cutting face as cuttings might be wedged by a negative rake of the cutting face against the formation to be cut.